Proposal Smoother Playback Scrolling

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Proposal pages help us get from feature requests into actual plans. This proposal page is about making improvements to scrolling while playing back or recording.
Proposal pages are used on an ongoing basis by the Audacity development team and are open to edits from visitors to the wiki. They are a good way to get community feedback on a proposal.


  • Note: Proposals for Google Summer of Code projects are significantly different in structure, are submitted via Google's web app and may or may not have a corresponding proposal page.

The Problems

These problems occur only when "Update display while playing" is checked in Tracks Preferences

  1. If you scroll right while playing, when the playback cursor bumps the left edge of the track waveform display the ruler can get out of sync with the waveform. Playback then corresponds to the time indicated in the ruler, not the position of the cursor in the waveform. Behaviour seems to be different on Mac versus Windows
  2. Display update while playing could be described as "klunky". The waveform display jumps every time the playback cursor reaches the right edge of the waveform display. This is currently a Feature Request:
  • Smoother Track scrolling on Playback: Keep the cursor in one place but move the track - gives smooth visual playback without continual cursor back and forth (14 votes)
    • As selectable option which is on by default in case of slower systems.
    • Or still allow cursor to move, but scroll smoothly when it reaches about 15% from the right and place cursor 15% from left (1 votes).

Developer / QA Backing

Bill W

Discussion

Playback cursor de-synchronization

On Mac the following behaviour is observed:

  1. New Project
  2. Generate chirp amplitude 0 - 1 (so it's easy to see), any length but lets say 30 seconds
  3. New track, generate another chirp
  4. Drag chirp from second track onto first, delete first track
    - you now have two chirps each in its own clip with a clear boundary between them
    - the effect is not dependent on having two clips: you can join them if you want
  5. Skip to Start then zoom in so you can only see the first chirp
  6. Click Play and wait a few seconds
  7. Click and hold the right scroll button
    - eventually the playback cursor will bump against the left edge of the waveform display area
  8. Continue to hold the right scroll button for a second or two
    - note that the boundary between the two clips is no longer at the 30-second mark
    - playback corresponds to the timeline, not the waveform display
    - on the Mac tested, the boundary moves to approximately 29.5 seconds and stays there
  9. Click Stop
    - the waveform jumps back to where it is supposed to be.

On Windows: LL reports: This happens on Windows too, but with a slightly different visual effect at step 8. On Windows, you see the end of the first clip alternate between the 30 second mark about 29.5 or so.

On Windows and Linux: Gale reports: Actually I don't get desynchronisation on Win XP or Linux that I would call such. The end of the first chirp is rapidly flicking back and forth between about 30s and 29.5s. That corruption stops near the end of the second chirp when the playback cursor is able to travel freely past the left edge of the waveform as it approaches the end of the track.

Smoother Scrolling

Bill prefers the first option listed above - keep the cursor in the middle of the track display. This nicely simulates tape moving past a playback head (for those of us who remember such things).